Twitter announced today via their support account that animated GIFs are now officially supported on Twitter.com, Android and iPhone. Previously, users needed to upload GIFs via a third-party service, but now they can be uploaded and viewed directly to Twitter.
So far this only works at Twitter.com and through the official iPhone and Android Twitter apps, no word if support it coming to other devices or third-party apps.
Love them or hate them animated GIFs are part of the web as we know it, and most likely won't be going away anytime soon. If you're a Twitter user, they'll now be more in your face than before, so get ready.
Source: Twitter Support